High temperature electric heater for gases



April l5, 1969' R. PRETE HIGH TEMPERATURE ELECTRIC HEATER FoR GAsEs i: of 3 Sheet Filed July 26, 1966 xvi fzln. lli s INVENTOR.

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HIGH TEMPERATURE ELECTRIC HEATER FOR AGASES Filed July 2e, 196e sheet of s INVENTOR.

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HIGH TEMPERATUR-ELECTRIC HEATER FOR GASES Filed July'ze, 19e@ sheet 5 of s INVENTOR. l lelY/"A/ Pf? 7" v United States Patent O 3,439,149 HIGH TEMPERATURE ELECTRIC HEATER FOR GASES Ralph Prete, West Haven, Conn., assignor to the United States of America as represented by the Secretary of the Air Force Filed July 26, 1966, Sel'. No. 568,065

Int. Cl. F24h 3/04 U.S. 'Cl. 219-374 2 Claims ABSTRACT OF THE DISCLOSURE An electric heater assembly capable of`raising the temperature of a non-oxidizing gas, such as hydrogen, to a level on the order of 2500 C. includes a cylindrical molybdenum shell through which the gas to be heated ows. A plurality of closely spaced molybdenum electrical resistance heating wires are spirally wound transverse to the cylindrical axis of the shell and are supported by a plurality of spaced, longitudinally extending boron nitride vanes, thereby providing a large heating area to the gas. Gas is introduced into the shell through a manifold assembly attached to one end thereof. A casing surrounds the shell and the space between the casing and shell is lled with thermal insulation.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a heat exchanger for gases and, more particularly, to a forced convection, electrical resistance heater for raising a gas to a high temperature.

The technique for raising the temperature of a gas by passing it through an electrical resistance heat exchanger is well known in the art. Prior art heat exchangers are generally cylindrical in shape and have resistance wires strung parallel to their cylindrical axes. The gas is heated by these wires as it ows through the tube. The heating capacity of these prior art devices is limited to moderately high temperatures. Since the heater wires are stretched along the cylindrical axis, the high temperature limit is proportional to their axial length. For very high temperatures the heaters length becomes impractically long. Also, the materials used in these prior art heat exchangers cannot withstand high temperatures.

The electric heater of this invention is capable of raising the temperature of high heat compressible fluids to very high temperatures, of the order of 2500 C. This invention employs a unique heater element inside a cylindrical shell housing to provide a much shorter axial length than prior art devices. The novel heater element of this invention consists of several closely spaced wires that are spirally wound transverse to the cylindrical axis. Such a heater element configuration provides a large surface heating area to the gas as it passes through the heater housing.

The heater element of this invention is designed to have a high resistance so that it may be energized by a high voltage to provide high power while requiring low current. This permits the design of a high power, high efciency gas heater since losses in an electrical heater are proportional to the square of the current.

It is an object of the present invention to provide an improved electric gas heater that will heat a gas flowing therethrough to a high temperature within a small distance.

Another object of this invention is to provide an improved electric gas heater having a heating element which ICC has a high resistance and requiring a low current with high voltage energization.

Other objects and novel features will become apparent fromthe following specifications and accompanying drawings wherein:

FIG. 1 is an axial section view of an improved electric heater for non-oxidizing gases embodying the invention;

FIG. 2 is a transverse vertical section taken along line 2-2 of FIG. 1 and viewed in the direction of the arrows;

FIG. 3 is a transverse vertical section taken along line 3 3y of FIG. 1 and viewed in the direction of the arrows; and

FIG. 4 is a transverse vertical section taken along line 4-4 of FIG. 1 and viewed in the direction of the arrows.

Referring to the drawings, 10 denotes a hollow cylindrical casing made preferably of stainless steel. One end of casing 10 is secured to closing member 11, as by welding or the like at 12. Stainless steel hollow cylindrical casing 14 is mounted to the other end of casing 10 by bolts 15 and 16.

The inner wall of casing 10 is provided with a snugly fitting tubular lining 13, made of insulating material.

Cylindrical shell 17 is located in a centralized position within casing 10. One end of shell 17 projects beyond flange 11 and is secured to closing member 11 at 18, as by welding or the like. The other end of shell 17 is secured at 20 to flange 19 as by welding. Bolts 21 and 22 extend through casing 10 and threadably engage flange 19. Cylindrical shell 17 and flange 19 are made of a material having varying temperature characteristics, preferably molybdenum.

Shell 17 is the housing for the heater element. FIG. 2 shows' a cross-sectional view of the shell housing and heater element. Referring to FIG. 2, there is shown the termination of six spirally wound molybdenum resistance wires 23 at one end of metal rod 29 (FIG. 1). The wires 23 are soldered together at the termination. Bolt 25 which is threadably engaged to rod 29 holds the wires 23 i-n place between washer 26 and the end of the rod 29. Rod 29, bolt 25 and washer 26 are all preferably made of molybdenum or an equivalent high temperature material. The six spirally wound wires 23 are closely spaced apart by means of eight vanes 24 made of electrical insulating material, preferably boron nitride. In FIG. l, the wires 23 are omitted so that the vanes 26 can -be clearly illustrated.

In FIG. 1, there is shown the lateral view of two of the eight vanes 24. Each vane 24 has lthree holes per row with the holes of alternate rows forming a straight line parallel to the cylindrical axis. Thus, there are six columns of holes which run parallel to the cylindrical axis. Each wire 23 is spirally wound along the cylindrical axis and threaded through the holes along one of the corresponding columns in each vane.

Vanes 24 are securely mounted in symmetrically arranged grooves located in washer 26 and annular member 31. To provide for the eight vanes shown in FIG. 2, there are eight grooves radially spaced every 45 in washer 26 and annular member 31. Eight vanes have been given for exemplary purposes only. Any number of vanes which would properly separate wires 23 would be included within the scope of this invention.

The space between lining 13= and shell 17, denoted as B in FIG. l, is lled with one of the well-known heat insulating materials.

Referring to FIG. 3, there is shown a cross-sectional view of chamber A where the gas enters the heating housing 17. The gas is forced into chamber A through three channels 27 which are depicted in FIG. 3 as three openings 27.

FIG. 3 also shows the connection of wires 23 to threephase terminals 30. One of these terminals 30 is shown 3 in FtIG. 1. As shown, two adjacent wires 23 are coupled to each terminal 30.

The gas is also forced through channel 28 and flows along molybdenum rod 29. By reference to FIG. 4, there is shown the manner in which rod 29 is supported centrally in channel 28.

FIG. 4 depicts a cross-sectional view of the manifold construction which couples entrance tube 32 to the heater housing. The gas to ibe heated flows from tube 312 to channel A via channels 27 and 28. Pipe 33 serves as a supporting member.

In operation, a three-phase, high-voltage source is connected to terminals 30 to provide a low heating current to flow through high resistance Wires 23. At the same time, a non-oxidizing gas, such as hydrogen, is introduced into chamber A and is gradually heated to a high temperature as it passes through channel 24. Using the heatin-g device of the present invention, dry hydrogen has been heated to 2500 C. at mass flow up to .04 lb.m./ sec. High temperatures of such magnitude are attainable for all nonoxidizing atmospheres.

The embodiment shown in FIGS. 1 to 4 illustrates the heating element wires 23 connected to three-phase terminals 30. However, it is within the scope of this invention that the wires could be connected to any high voltage source, either A-C or D-C.

It can now be seen that one of the important features of this invention is the arrangement of a plurality of closely spaced, spirally wound, electrical resistance `wires within a heater housing so that a gas flowing therethrough will be heated to a high temperature within a very short distance of ow. I

-Other important features of this invention have been shown to be the manner of insulating the heater housing to maintain it at a high temperature, and the selection of materials used in the heater housing that can withstand the high temperatures attainable by the unique heater element of this invention.

What is claimed is:

1. An electric heater for raising the temperature of gas owing therethrough comprising:

(a) a cylindrical shell for housing a heater element and having a passageway for said gas which is open at the inlet end and outlet end;

(b) a ttirst hollow cylindrical casing enclosing said shell having a substantially larger inner diameter than said shells outer diameter;

(c) an insulating material lling the space between said shell and casing;

(d) a second hollow cylindrical casing mounted at one '4 end in sealed relationship to said ,first casing at said inlet end and having a substantially larger inner diameter than said shells outer diameter to form a large chamber;

(e) the other end of said second casing being closed by a cover member having several small and large openings;

(f) an electrical terminal means extending through each of said small openings into said large chamber;

(g) means for electrically insulating and sealing each of said electrical terminal means within their respecti-ve small openings;

(h) means for channeling the gas to be heated through each of said large openings into said chamber; (i) a metallic rod centrally positioned and supported within said cylindrical shell having a diameter substantially smaller than the inner diameter of said shell vand extending essentially the length of the large chamber defined by the second casing and the length of the cylindrical shell;

(j) several thin electrically insulating vanes projecting radially from said rod and extending essentially the length of said cylindrical shell and said large chamber;

(k) several spirally wound electrical resistance wires extending essentially the length of said vanes that are each wound transverse to said rod and through separate holes in said vanes in such Ia manner as to closely separate said Wires from each other; and

(l) means for connecting the end of each of said wires at said inlet end to the said terminal means and means for connecting the ends of said wires together at said outlet end.

2. The electric heater as dened in claim 1, wherein:

(a) said shell, rod and electrical resistance wires are made of molybdenum; and

(b) said vanes are made of boron nitride.

References Cited UNITED STATES PATENTS 1,038,410 9/1912 Mies 219--375 1,520,241 12/1924 Happe 219-376 X 2,120,583 6/1938 Timberlake 219--380 X 3,210,927 10/1965 Brinich et al 219-374 X ANTHONY BARTIS, Primary Examiner.

U.S. Cl. XR. 

